Stupid Careless Mistake

I had State Variable Control today, the much-dreaded paper, which is not so much of a worry actually if you have done all the papers and examples etc. But I really don't like dealing with matrices.

Chose the easiest (and quickest) 3 questions, 20 marks each: 3, 4 and 5. But in Question 5 I encountered a problem: the inverse matrix was not nice to form. My denominator was s2+s+1 which was not factorisable... something was wrong. So after deciding that the last 6 marks were a bit risky, with the the previous sections not too stable, I ditched it for question 1. Now the problem was that question 1 is matrix-intensive and needs quite a lot of solid calculation. The smart candidate would avoid doing it. Plus I had to define the system states so it's not confirmed that I will get it right. The only indication whether I was on the right track would be when I came to the last 10 marks in finding the answer to u(t). If I found that my matrix was invertable with the denominator easily split into factors (for partial fractions) it would normally mean I was right since the question is not doable if we had an unfactorisable denominator! So I got the factorisation done (yay) but there was no time to evaluate the entire matrix (plus integration). And I plugged the wrong system states in which means the first term should have been 0 instead of my value, something like (4/3).

After the exam I found out my elementary mistake in q5.... and after counting, I conclude that my marks would probably not differ by much no matter which question I attempted in the end! Both would score ard 14 marks... wasted my time. Talk about the mark maximisation theorem that I professed to the secondary school students in the college I was attached to last semester! Ugh...

(But to be frank, I have never been so far in a question before and still decide to ditch it... guess you have to try some things once in your life sometimes)